Definition of pH
pH is a measure of the hydrogen ion concentration in a solution, specifically the activity of hydrogen ions (H⁺). It quantifies how acidic or basic (alkaline) a solution is. The pH value is defined as the negative logarithm of the hydrogen ion concentration: pH = -log₁₀[H⁺]. Lower pH values indicate higher acidity, while higher values indicate greater basicity.
The pH Scale and Key Principles
The pH scale ranges from 0 to 14. Solutions with pH less than 7 are acidic, containing more H⁺ ions than OH⁻ ions. A pH of 7 is neutral, as in pure water where [H⁺] = [OH⁻] = 10⁻⁷ M. Solutions with pH greater than 7 are basic, with excess OH⁻ ions. Each unit change represents a tenfold difference in ion concentration, emphasizing the logarithmic nature of the scale.
Practical Examples
In everyday applications, lemon juice has a pH of about 2, making it acidic due to citric acid. Seawater typically has a pH around 8, slightly basic from dissolved minerals. Battery acid can reach pH 0, highly corrosive, while milk of magnesia, used as an antacid, has a pH of 10, neutralizing stomach acid effectively.
Importance and Applications
pH measurement is crucial in fields like biology, where it affects enzyme function and cellular processes; environmental science, for monitoring water quality and ocean acidification; and industry, such as in food production to ensure safety or in pharmaceuticals for drug stability. Accurate pH control prevents damage to ecosystems and optimizes chemical reactions.